1. Field of the Invention
The invention concerns electrical connectors.
It is more particularly concerned with connectors having the following functional characteristics:
a large number of operating cycles (typically 5,000 to 50,000), which means that measures must be taken to prevent premature wear of parts rubbing together and to make the electrical contact members self-cleaning, PA1 large areas of contact, which means that the homologous moving parts of the connector must be able to provide satisfactory electrical contact over the full length of a relatively large insertion travel with relatively wide dimensional tolerances, PA1 moderate insertion and (end of travel) latching forces, as is usually the case with connectors where end of travel locking is provided by a mechanical member external to the connector proper: in this case the latching force must be limited (because it will be provided by the external member) and the connector must accommodate relatively wide dimensional tolerances (cf. the previous characteristic) because the mechanical precision of mating (mechanical approach of the mobile members) and that of the insertion travel depend on the external member rather than on the connector itself.
2. Description of the prior art
The cooperating members of a connector comprise at least one rigid conductor member which comes into mechanical and electrical contact with a flexible (i,e, elastically deformable) contact member relative to which it can move, These members are referred to hereinafter as the "rigid member" and the "flexible member" but in practise the rigid member is also called a "pin" or "male member" and the flexible member is then called a "socket" or "female member".
In a first type of connector shown in FIG. 1 the rigid member 1 extends in a longitudinal direction .DELTA. and the flexible contact member(s) 2 are substantially parallel to the direction .DELTA.. To make the electrical contact the rigid member 1 is moved in the longitudinal direction .DELTA., the effect of which is to push back the free end of the flexible member(s) in a transverse direction, i.e. in a direction substantially perpendicular to the direction .DELTA. (as shown in dashed outline in the figure).
This connector structure has several advantages.
First of all, it is possible to obtain a long travel without difficulty because the deformation of the flexible members (transverse separation) depends only on the diameter of the rigid member and the travel in the longitudinal direction .DELTA. may therefore be made longer without difficulty when designing the connector.
Secondly, because the length of the contact path (i.e. the locus of the successive points of contact over the length of the insertion travel) is equal to the travel of the connector, self-cleaning of the point of contact by rubbing is ensured without difficulty.
Finally, this type of connector requires only a moderate insertion and latching force: in FIG. 3 the curve I shows the F/d (insertion force/insertion length) characteristic of this type of connector. The curvilinear segment OA shows the force required to deform radially the flexible members 2; when the deformed position is reached there is a peak A whose amplitude may be limited by an appropriate choice of the cooperating shapes. Then, if insertion is continued (segment AB) the insertion force is substantially constant over all of the usable travel D.
However, this type of connector is subject to premature wear, precisely because the point of contact, which is practically fixed, travels a great distance along the rigid member because the length of the contact path is the same as the mechanical travel of the connector.
In a second type of connector shown diagrammatically in FIG. 2 and which is the type to which the invention relates the flexible contact member extends in a generally transverse direction substantially perpendicular (or strongly oblique) to the direction .DELTA. in which the rigid contact member 1 extends. Connection is then achieved by relatively simple end bearing on the free end of the flexible member which bends progressively as the rigid member 1 is inserted.
Because the length of the contact path is much reduced as compared with the previous example, wear is much reduced, improving durability. On the other hand, self-cleaning is much reduced because the contact path is reduced.
However, the major drawback of this type of connector is that it requires a relatively high insertion force, especially at the end of travel: in FIG. 3 the curve II shows the respective F/d characteristic. Note that after a small force (segment OA') which is that required to reach the point A' at which satisfactory electrical contact is provided, on further insertion of the rigid member the force required increases very rapidly (segment A'B') because of the progressively increasing resistance due to the lever arm of the flexible member, which is increasingly strongly loaded. Also, the usable travel D' is much reduced as compared with the previous example.
These drawbacks (high insertion force and reduced travel) are particularly troublesome in the applications mentioned above where the two members of the connector are latched together by a member external to the connector proper: the maximum force F.sub.max permitted for latching the connector is then very quickly exceeded; also, the relatively short travel D' cannot compensate adequately for dimensional tolerances and therefore requires very careful construction of the external latching member because it is the dimensional accuracy of the latter which determines the functional quality of the connector.
One object of the present invention is to propose a connector which remedies these various drawbacks and provides long travel, low insertion force and high reliability (low wear and self-cleaning).